1. Field of the Invention
The present invention relates to an improvement on or relating to an electromagnetic relay of the type in which relay contacts are actuated by a movable armature in response to energization and deenergization of an electromagnetic coil wound on an iron core.
2. Description of the Prior-Art
Heretofore, there has been known an electromagnetic relay in which a movable armature is rotated under the magnetic force produced by an electromagnet to thereby switch or change over a contact mechanism. This type relay, however, suffers from various drawbacks. For example, the magnetic force produced by the electromagnet is not utilized effectively but undergoes considerable loss. It is difficult to realize the smooth operation in the balanced state.
Further, in the electromagnetic relay, the contact mechanism is acommodated within a space defined by an electrically conductive layer which is connected to the ground with a view to attaining high electrical isolation and improving the high-frequency characteristics. More specifically, a room for accommodating the contact mechanism is formed in a molded synthetic resin block defining the contact accommodating room being coated with an electrically conductive layer through plating, evaporation or the like process.
The metallized projections are used as the earth terminals to which lead wires are soldered when the relay is mounted on a substrate for a printed circuit. In the soldering process, molten solder material heated at ca. 260.degree. C. remains in contact with the metallized projections for about ten seconds. In case the solder material is heated at 350.degree. C., the contacting duration will be about five seconds. Accordingly, if the base provided with the terminal projections is formed of a conventional inexpensive resin material which is likely to undergo thermal deformation at a relatively low temperature, the resin material is easily thermally expanded (bulging) or fluidized to rupture the metal layer, eventually involving destruction of the earth terminal.
As an approach to dispose of the difficulty mentioned above, there is known a proposal illustrated in FIG. 1 of the accompanying drawings. Referring to the figure, a numeral 60 denotes a base made of a synthetic resin, 61 denotes a projection formed integrally with the base 60 and used for the earth terminal, and 62 denotes an electrically conductive film deposited on the base 60 and the projection 61 through plating with a sub-layer 63 being interposed.
In the structure shown in FIG. 1, a depression 64 is formed in the bottom end of the projection 61. This depression 64 is not coated thick with the electrically conductive layer 62 in an attempt to allow the resin material to expand or be fluidized at this portion 64, for thereby preventing the metallic layer 62 from being ruptured. However, in practice, when the earth terminal 65 is to be implemented thin such that the foot portion of the projection 61 is, for example, on the order of 0.8 mm in diameter with the top being ca. 0.3 mm before metallization, the finished cylindrical earth terminal of ca. 0.9 mm in diameter tends to be deposited with an increased amount of electrically conductive material at the tip 61. In other words, a great difficulty is encountered in realizing the depression 64 in the tip of the projection 61 in the manner shown in FIG. 1, which in turn means that it is difficult to positively protect the earth terminal 65 from destruction when it is heated upon soldering which results in, to a serious disadvantage.
As another attempt to solve the above problem, there is conceivable a method illustrated in FIGS. 2(A) and 2(B). More specifically, the free end portion 67 of the earth terminal 65 is cut away along a broken line 68, for preventing the rupture of the electrically conductive layer 62. In that case, however, drops of the molten resin material will contaminate other parts of the relay. Besides, the cutting requires an additional time consuming process.
Furthermore, in the hitherto known electromagnetic relay, the assemblying of the electromagnet and a core frame on a base requires a troublesome and time consuming procedure. For example, the core frame is first secured to the coil spool of the electromagnet by rivetting and subsequently depending projections formed in collars of the spool are fitted in the apertures formed in the base to be fixedly secured to the base by thermal rivetting or by using a bonding agent, requiring thus at least two assembling steps.